1. Field of the Invention
The present invention relates to apparatus for combining the components of a material in building and civil engineering operations and particularly for material for use as backfill in roadwork trench excavation.
2. Description of the Related Art
A process of recycling site-won spoil to provide a material suitable for use as a backfill is described in international patent application PCT GB01/03083 filed on 9 Jul. 2001 by the present applicant. The manufacture of such a material requires the mixing of a predominantly non-granular cohesive material such as a clay soil with powder components in specific proportions. These powder components may be lime, cement and/or pulverised fly ash (PFA) also known as pulverised fuel ash.
Technical Problem
Technical problems arise in ensuring a good distribution of the powder components within the cohesive material and also in producing a material which has consistently proportioned ingredients.
The earlier application, which was unpublished at the priority date of this application, proposed a machine in which a mixing screw is used to amalgamate the components. Whilst satisfactory, it is possible for such screws to become clogged when used with cohesive materials such as heavy clay and therefore the present invention proposes an alternative approach in which the cohesive components are broken up prior to the addition of the powder ingredients.
More specifically the present invention provides a machine for recycling site-won spoil comprising predominantly non-granular cohesive material from an excavation for immediate re-use as a backfill, comprising means for receiving excavated cohesive material, means for adding a measured amount of powder material, mixing means comprising a pan mixer having a rotary blade or vane for thorough mixing the components and discharging them from the machine, and first and second means for breaking up the cohesive material before it enters the mixing means, the first breaking means being in the receiving means.
Preferably mixing is then carried out by vanes operating within a pan mixer, which is less liable to clogging. Preferably some of the lime is also added at an intermediate stage while the spoil is being broken up.